Bantam Cages

I have several different kinds of bantams and have them in individual pens inside our barn in one stall. The cages are metal wire - the bottom is covered with shingles, keeps toenails worn off, with shavings on top of that.

My question is what is best for breeding pairs, trios, etc. I can't keep all of them outside in runs - I would have to have too many. I have the banty room well lit and lights are on all day - 7am to 7pm. The pens I have are many different sizes, the smallest is 2' x 2' square. I have a pic of some of them - it does take time to feed and water them but that's part of it.

Does anyone have the same type setup? If so, what size works best for a pair, trio, etc.